This invention relates in general to methods of producing inorganic polymer hybrids. More specifically, this invention relates to methods of producing inorganic polymer hybrids by inducing nanoscale exfoliation of an inorganic component.
Hybrid composites of polymer and inorganic components such as clays and mica have been described in the prior art as having improved mechanical properties. Such composites are referred to as nanocomposites, which reflects the dispersion of nano-scale particulates of the inorganic component of the hybrid in the polymer matrix. There are references in both the patent and scientific literature of various clays, which have been modified and combined with polar polymers such as polyamides to form nanocomposite materials.
However, the introduction of nanoparticles into nonpolar polymers such as polyolefins to form a nanocomposite is a much more difficult task due to incompatibility of the polar nano particles with the nonpolar polymer. This incompatibility often causes non-uniform distribution of the inorganic component throughout the polymer, leading to less than optimum performance. Typically, this difficulty is overcome by combining the nonpolar polymer with a similar, but chemically modified polymer (e.g. polypropylene-g-MA), which contains polar functionality to act as a compatibilizer molecule. The polar functionality of the modified polypropylene is able to interact with the polar character of the nanoparticle, and the nonpolar portion of the modified polypropylene interacts with the polypropylene matrix. Presumably, the interaction between the two polar functionalities provides both exfoliation and compatiblization, thereby resulting in a nanocomposite with uniform distribution of the nanoparticles.
U.S. Pat. No. 5,973,053 describes a layered composite clay material wherein organic onium ions and primary and secondary organic xe2x80x9cguestxe2x80x9d molecules are introduced into the interlayer space to increase the interlayer distance. The introduction of the organic onium ion acts to increase the compatibility of the clay with polymer and facilitate the dispersion of the clay in the hybrid composite.
In xe2x80x9cFactors Controlling Mechanical Properties of Clay Mineral/Polypropylene nanocompositesxe2x80x9d, Journal of Materials Sciences 35 (2000) 1045-1050, Oya et al describe intercalating a clay with a polar monomer, diacetone acrylamide and maleic acid modified polypropylene as a compatibilizer. This organo-clay was then mixed with conventional polypropylene to prepare a nanocomposite. In xe2x80x9cPoly(propylene)/organoclay nanocomposite formation: Influence of compatibilizer functionality and organoclay modificationxe2x80x9d, Macromolecular Material Engineering 275, 8-17 (2000), Reichert et al describe the use of alkyl amines as intercalating agents in silica clay with and without the use of maleic anhydride modified polypropylene.
It would be desirable to provide a method for making a nanocomposite with uniform dispersion of the inorganic component that does not require the use of compatibilizers. It would still further be desirable to provide a method for making inorganic polymer hybrids using hydrotalcites that are self- and/or reversibly exfoliating such that the hydrotalcites could be produced and stored for later use. It would still further be desirable to provide hydrotalcite polymer nanocomposites with improved mechanical properties and method for producing them using modified or unmodified hydrotalcites.
The present invention provides a method for producing inorganic polymer hybrids with improved mechanical properties and even dispersion of the inorganic material in the hybrids. The method provides for inducing exfoliation in an inorganic material having a layered structure, and combining said exfoliated inorganic material with an emulsion comprising at least one molten polymer. The method of the current invention takes advantage of the interaction between jag inorganic materials and solvent molecules that are introduced into, or associated within the layers of the inorganic material to induce exfoliation of the inorganic material.
In one embodiment of the present invention, the inorganic material is added to a solvent to create a suspension, slurry, or paste. In this embodiment, self-exfoliation occurs in the solvent, and the resulting suspension, slurry, or paste is then combined with the molten polymer to create an inorganic polymer hybrid.
In another embodiment of the present invention, exfoliation of the inorganic material is induced by rapid vaporization of solvent molecules trapped in or associated with the layers of the inorganic material when the dry inorganic material is combined with the molten polymer to create an inorganic polymer hybrid.